Denon AVR crossover doesn't seem to work for main speakers

[KMO]

Furthermore, when listening to music, the subwoofer will only get a signal of subwoofer mode is set to "LFE+Main". If LFE only, then the subwoofer only gets LFE effects (like in Dolby or DTS)

Incorrect. If the speakers are set to SMALL, and you're not in a DIRECT mode the subwoofer will get redirected bass. There's no need to select LFE+Main.

• LFE: Subwoofer plays LFE and bass (below crossover frequency) from speakers set to SMALL
• LFE+Main: Subwoofer plays LFE and bass (below crossover frequency) from all speakers

So if LFE+Main is active then content below the crossover frequency is being doubled up to sub and LARGE speakers. You don't normally want that. But then, if all your speakers are SMALL, as they probably should be, the setting doesn't matter.

Oh, and DIRECT overrides the above because crossovers are disabled, so the sub can only play LFE.

The option name is as clear as mud. It's possible the option is a marketing sop for people who want to set their speakers to LARGE (because who wants to think they have small speakers?) but then find there's no crossover, so no subwoofer output.